1. Field of the Invention
The invention relates to flow velocity measurements in pipes and conduits carrying water, sewage, and other fluids.
2. Description of the Related Art
There are many environments where information regarding the mass and/or volume flow rate of a fluid through a conduit is valuable. These include irrigation, residential water distribution, sewage treatment, and many others. Although various types of mechanical flow meters have been used, acoustic methods are often preferable because of their ease of installation, lack of interference with the flow, and long term reliability. One type of acoustic flow measurement device utilizes the Doppler effect to measure flow speed. With these devices, sound energy is reflected off of particles moving with the flowing fluid and is received by a receiving transducer. Sound energy received by the receiving transducer is frequency shifted due to the relative motion between the particles and the receiving transducer. The frequency shift is related to the flow rate of the fluid.
Several systems using Doppler effect based flow measurement have been proposed. One such system is described in U.S. Pat. No. 5,020,374 to Petroff et al. With the system described in this patent, separate transmit and receive transducers are placed in the fluid flow, and a continuous wave signal is output from the transmit transducer. Because the transducers are placed within the flow, installation is difficult and labor intensive, especially if installation is desired in a conduit with fluid flow already present. Furthermore, due to its continuous wave nature and the fact that the Petroff et al. device produces a quickly spreading beam of acoustic energy, an accurate measurement of even an overall average fluid velocity in the pipe is at best difficult and often impossible to obtain. There is therefore a need to develop flow measurement techniques which are more accurate than have been previously available.
With embodiments of the present invention, flow rates of fluid flowing through pipes or other conduits are measured in a relatively convenient and accurate manner. In one embodiment, the invention comprises an assembly for routing fluid and measuring a flow rate of the fluid. The assembly comprises a conduit comprising a wall defining a fluid flow path, said wall having an opening therein, an acoustic transducer assembly sealed into said opening and a signal generator coupled to said acoustic transducer assembly and configured to electrically drive said acoustic transducer assembly.
In another embodiment, an apparatus for measuring the flow rate of fluid in a pipe comprises an acoustic lens, a plurality of acoustic transducers coupled to a lens so as to emit acoustic energy through a surface of the lens, and a signal generator configured to electrically drive the acoustic transducers at a selected excitation frequency so as to produce sound waves in the fluid having a selected wavelength, wherein the acoustic transducers have a characteristic dimension that is much larger than the selected wavelength.
Methods of fluid flow measurement are also provided. In one embodiment, such a method comprises positioning a plurality of acoustic transducers in an opening in the wall of the pipe, emitting a plurality of narrow beam pulses of acoustic energy into fluid flowing within the pipe using the transducers, detecting doppler shifted reflections of acoustic energy from regions within the fluid, and determining total fluid flow through the pipe at least in part by analyzing the doppler shifted reflections.